Core samples from subterranean hydrocarbon formations are routinely tested for permeability and to determine the flow characteristics of possible flooding operations in such formations. In running coreflooding experiments, the sample is first saturated with a liquid such as oil, then placed in a sample holder where it is exposed to a pressurized fluid. The pressurized fluid, which may be gas, such as helium, or a liquid, such as a foam, displaces the saturating liquid, and the fluid mixture is then collected and separated into its liquid and gaseous components for measurement and analysis.
Automated gas-liquid permeameters have been developed for continuously collecting and instantaneously measuring produced fluids, but these are relatively expensive and not always available for use. More often, the produced fluids from coreflooding experiments run under back pressure are incrementally collected by one of two methods. One method requires fluid to be collected at atmospheric pressure downstream of the back pressure regulator in the system. Under these conditions both the liquid and gas phases of the fluid pass through the back pressure regulator which, due to the varied viscosities of the liquids, gases and emulsions passing through, tends to repeatedly build and release pressure. As a result, the pressure in the system fluctuates during a test procedure, which lessens the accuracy of pressure measurements.
In another method all the liquid phases are collected prior to the fluid reaching the back pressure regulator, allowing only the gas phase to pass through the back pressure regulator. The gas phase is then collected downstream of the back pressure regulator or at atmospheric pressure. The collected liquid and gas phases can then be separately measured and analyzed. A problem that can be encountered in this method, depending on the particular test equipment involved, is that the production tube that delivers liquid to the collection receptacles is often required to be so long that it interferes with the operation of the stepper motor employed to sequentially align the production tube and the collection receptacles. Another problem is the need to minimize production dead volume in test equipment employed in carrying out this method.
It is therefore an object of the present invention to overcome these problems by providing an improved mechanical arrangement for delivering and collecting fluid from a coreflood sample under back pressure conditions.